The valve mechanisms of U.S. Pat. Nos. 3,913,327 and 5,003,780, respectively entitled "Flow Sensitive Valve Mechanism" and "Fluidic Valve Mechanism" and respectively issued Oct. 21, 1975 and Dec. 28, 1989 in the name of the inventor of the invention herein disclosed and claimed provide the background for this invention.
The first noted patent disclosure provided a fluid flow sensitive valve member in a valve chamber between a pressurizing chamber and an outlet port of a master cylinder. A compensation port leading to a fluid reservoir also opened into the valve chamber. The valve member had flow sensitive fins angularly positioned in the flow path of fluid flowing through the valve chamber. The valve member had a valve body with a guide pin extending upwardly from the body into the lower portion of the compensation port to maintain the valve member in lateral position relative to the valve seat formed at the bottom of the compensation port. That seat could be engaged by the valve body to close off the compensation port when the valve was moved upwardly, and could be disengaged to open the compensation port when the valve was moved downwardly. A first valve member flow sensitive fin, formed on the valve body, was positioned near the port to the pressurizing chamber and was angled so as to deflect the fluid downwardly when fluid pressurization in the pressurizing chamber occurred. The impact force of the fluid acting on the fin moved the valve member upwardly to close the compensation port. The fluid flowed under and around the valve member, passing into the outlet port and pressurizing the appropriate mechanism to be operated by the fluid pressure.
A second valve member flow sensitive fin, also formed on the valve body and parallel to the first fin, was positioned near the outlet port so that when the pressure was released, the fluid flowing back into the valve chamber from the outlet port impinged on the second fin, forcing the valve member downwardly and opening the compensation port. The returning fluid coming back through the outlet port flowed through the compensation port into the fluid reservoir and also past the valve member back into the pressurizing chamber. The valve member was made of a material having a specific gravity slightly greater than the specific gravity of the fluid used so that the assembly would be self-bleeding.
In the second noted patent disclosure, the valve mechanism has features that provide positive functional actions that cannot be deviated and are necessary because of the extremely sensitive flow conditions in the mechanism. The disclosure shows structure which controls the valve member during all fluid flow conditions, and particularly during post-release fluid flow situations, to force the valve member to the proper position for each function.
These functions include (1) sealing the reservoir port at the minimum flow conditions occurring with very slow apply rates; (2) causing all return flow coming back toward the reservoir and the master cylinder upon release of the master cylinder to enter either the master cylinder bore or the reservoir; and (3) causing all post-release return flow to enter the reservoir. Furthermore, during certain of the final release instantaneous positions, or during post-release flow conditions, to allow reapply demand imposed on the system to take control of the valve so that a safe, substantially instantaneous reapply is obtained.
The structure of the second noted patent disclosure which accomplishes this includes a valve member providing an arrangement for sealing and opening the reservoir port, either as a subassembly of a valve mechanism or as a single component mechanism. The valve member, or the entire valve mechanism, is referred to as a fluidic valve, indicating that it is operated by and controls fluid flows and pressures by flow of the fluid itself. The disclosed valve mechanism is a multi-part assembly, and it includes the valve member and a positive valve member positioning device.
One such positive positioning device or interface structure is disclosed as a strut-like pivotable lever formed from sheet material, preferably a metal such as stainless steel, and having flow impingement areas which are acted upon by various fluid flows to move the lever so that it either prevents or permits the valve member to close the reservoir port. Another disclosed device is formed as an integral part of the valve member which cooperates with a receiving chamber and is acted upon by various fluid flows to obtain similar results.
Advantages obtainable by employment of the fluidic valve embodying the invention disclosed in the second noted patent, and also in the improvement invention herein disclosed and claimed, are numerous. They include:
(1) Reduction in length of a master cylinder. The secondary seal can be eliminated, giving as much as a forty percent reduction in master cylinder length. Further length reduction is attainable by substantially reducing the return spring loads because high return spring loads are not necessary. PA1 (2) With shortened master cylinders, the technique of recessing the master cylinder axially within a typical vacuum power brake booster will result in having very little of the master cylinder protruding axially beyond the booster, taking up much less space in an automotive engine compartment than a booster-master cylinder combination in which most if not all of the master cylinder protrudes axially beyond the booster. PA1 (3) Remote reservoirs can be used in various hydraulic actuating and release systems. For example, they may be used in a hydraulic brake system without the added cost penalty of additional fluid lines and fittings to connect the remote reservoir to the master cylinder. The fluidic valves can be used to feed brake fluid at any high point in the line in the pressure system between the master cylinder and the vehicle brake assemblies. This, in combination with the very short booster-master cylinder assembly, provides much more latitude in brake system routing and design without added complexity or cost penalty. The same advantages apply in a hydraulic push-pull cable system used for two-position or other multiple position control of a mechanism. Such mechanisms include air flow doors in heating and air conditioning systems for vehicles as well as buildings or sensitive equipment, and vehicle parking brake cable connections between a parking brake pedal and the parking brake itself. PA1 (4) Silicone brake fluid can be more readily used with the fluidic valves because very little negative pressure is created on any release stroke, and makeup or compensation fluid to the system takes place with very little fluid aeration. PA1 (5) Air removal is a natural with the fluidic valve. Any air bubbles in the hydraulic fluid system, commonly caused by fluid aeration, are quickly cleared into the reservoir, eliminating that undesirable cause of fluid compression which when the brake system is actuated contributes to brake loss. PA1 (6) Master cylinder seal life is improved since the seals do not have to run over bypass holes in the master cylinder bore. This totally eliminates the cutting of the seal or cup lips by the bypass holes. Since cup lip seals are not needed, intermittent failure of the cup seals through hydroplaning is also eliminated. In prior master cylinder designs using lipped cup seals, the lips had to collapse to allow makeup fluid to pass into the system. On rare occasions, this feature allowed hydrostatic shock to support the cup lips away from the master cylinder bore. This resulted in what is known in the brake industry as a phantom failure. The problem would be evident when both pressure chambers were affected in this manner at the same time, giving a complete loss of braking action on a master cylinder actuating stroke, yet would appear to fully recover on the next actuating stroke with no structurally apparent reason for the intermittent failure when the master cylinder was examined. PA1 Eliminating the bypass holes also eliminates the need for critical location of the bypass holes. This simplifies manufacture, since only bore surface finish and stroke length remain to be controlled. The outlet holes are considerably larger in diameter than bypass holes, and position tolerances for these holes are relatively liberal. With master cylinder bores 40% to 50% shorter because of elimination of the secondary seals and the bypass holes, only one seal being necessary per pressure chamber, machining is reduced. Shorter bore depths are more easily machined. PA1 (7) A serious concern in failure mode studies of master cylinders is the presence of particles of foreign material in the brake fluid circuits. Such materials can cause seal and bypass orifice failures once it is in the pressure side of the brake system. Materials commonly found are small plastic flashing segments, small metallic particles, and small seal material which originated as flashing or because of the nipping of the seal cup lips.
To provide an absolute worst case test, particles of materials having about the same density as brake fluids, lighter than brake fluids, and also heavier than brake fluids, were packed into fluidic valves embodying the invention disclosed and claimed in the second noted patent. Consistently after several apply cycles all of the foreign material would be blown from the valve chambers into the reservoirs, leaving the valves purged for the next apply. While purging the valves of the foreign materials, only a slight pedal travel loss occurred, with two to five pedal strokes purging even the packed valve chamber. Obviously, such a packed valve chamber is an artificial contrivance, and is a much worse condition than that found at any time in actual practice.
With the fluidic valve made of polyamide, a material only slightly more dense than brake fluid, polyamide flash debris is a possibility. Such debris will float and move around in the brake fluid with very little fluid flow. Tests showed that even if a large piece of polyamide flash with small entry dimensions should occlude the valve seat area, the valve sealing performance is diminished in that one valve chamber because the compensation port acts as a restrictive orifice for only one apply, only for that valve chamber, and not both chambers. The next apply was consistently found to purge the valve as the debris entered the reservoir.
The flow energy in the fluidic valve is immense, even on the slowest of master cylinder apply operations. It is this intense flow energy that keeps the entire valve area clean and clear of debris. Tests with extremely slow pedal applications by a machine in a very uniform manner, on the order of as much as thirty seconds to one minute, which are well beyond the slowest of pedal applications by a human brake operator in a vehicle, still closed each fluidic valve in less that 0.010 inch pedal travel loss for a manually actuated dual chamber master cylinder. When applied in a typical manner by typical drivers, only 0.010 inch pedal travel loss is common with a dual chamber master cylinder using fluidic valves disclosed in the second noted patent.
Considering that this is travel loss at the pedal itself, and that there is commonly about a 4:1 to 7:1 pedal ratio in vehicle service brake pedal arrangements, the fluidic valve for the primary pressurizing chamber is closed with a minuscule amount of master cylinder primary pressurizing piston movement. Assuming a 5:1 pedal ratio, the typical 0.010 inch pedal travel required to close the valve translates into 0.004 inch movement of the primary pressurizing piston in the pressurizing direction to close the valves for both the primary and secondary pressurizing pistons. With typical bypass holes and lipped cup seals, the primary piston movement required to move the primary cup seal lip to cover the primary bypass hole is about 0.10 inch. With the same 5:1 pedal travel ratio this translates to pedal travel loss of about 0.5 inch when a manually operated (no brake booster) system is employed. It is apparent that the use of the fluidic valve reduces the pedal travel loss by about 0.49 inch. This is a 50:1 improvement. When expressed in percentage improvement, this is a 5,000% improvement. A typical dual master cylinder with fluidic valves instead of cup seal lips, bypass ports and compensation ports has been found to provide as much savings in pedal travel loss as a quick take-up master cylinder, but without the complexity and losses of the old stepped bore quick take-up design.
When the typical current production dual master cylinder with cup seal lips, bypass ports and compensation ports is actuated by the typical production vacuum-suspended power brake booster, about the first one-eighth (0.125) inch of foot pedal travel acts only to open the booster air valve to begin to permit air at atmospheric air pressure to enter the variable pressure power chamber or chambers of the booster so as to begin to create a booster pressure differential across the booster power piston or pistons which in turn generate a booster output force delivered to the master cylinder. This assumes that there are no pedal linkage travel losses due to loose connections or pivot joints. The booster output force builds up as the booster power pressure differential increases and acts through a push rod to begin movement of the primary pressurizing piston of the master cylinder. This movement also moves the primary cup seal lip axially until it passes over the bypass port, closing that port. Only at this point of actuation is the master cylinder then ready to begin pressurizing brake fluid in its primary pressurizing chamber. Pressure in that chamber, as it builds up, then acts on the secondary master cylinder pressurizing piston, beginning the movement of that piston and the secondary cup seal lip on its forward end and culminating in the closure of the secondary pressurizing chamber bypass port. At this point both master cylinders have their bypass ports to the reservoir closed so that further movement of the booster output push rod will cause brake fluid to be pressurized in both master cylinder pressurizing chambers and that pressurized fluid delivered to the brake circuits connected to those pressurizing chambers to begin brake actuation. Further brake pedal movement in the actuating direction required to close both of these bypass ports from the rest or brake released position requires about one-half to five-eighths inch (0.5 inch to 0.625 inch) pedal travel. Thus the typical total foot brake pedal movement required just to begin to generate pressurized brake fluid in the master cylinder pressurizing chambers is about five-eighths (0.625) inch to three-fourths (0.75) inch, assuming no travel loss in the mechanical connections of the pedal assembly. In one regular production vehicle installation where this has been carefully measured, the total required brake pedal travel has been about three-fourths (0.75) inch.
In the same installation, but with the typical dual master cylinder and its reservoir now having fluidic valves embodying the invention herein disclosed and claimed to control the compensation ports instead of using axial movements of the cup seal lips to close the compensation ports, the same one-eighth (0.125) inch of pedal travel is still required to actuate the power brake booster so that it begins to move its output push rod in the actuating direction. At this point, it takes only sufficient additional brake foot pedal travel to obtain about two thousandths (0.002) inch master cylinder piston travel required to close each valve, or four thousandths (0.004) inch travel to close two valves for the dual master cylinder. With a 5:1 brake pedal ratio, this translates into the required approximately one one-hundredth (0.010) inch additional pedal travel in the pressurizing direction to close the valves for both the primary pressurizing circuit and the secondary pressurizing circuit. This means that, even with the booster-required pedal travel of one-eighth (0.125) inch, the total brake pedal travel to begin pressurizing brake fluid in both master cylinder pressurizing chambers is one hundred thirty-five thousandths (0.135) inch for typical brake applications.
Comparing this with the current production brake foot pedal travels of about three-fourths (0.75) inch with a vacuum-suspended power brake booster and a current production dual master cylinder, the improvement is about 555% when using the fluidic valves of the invention.